Pipettes for handling precise quantities of liquid are well known in the art. A typical manual pipette is described in U.S. Pat. No. 3,766,784 to Walker. It is common, as illustrated in FIG. 1 of the Walker patent, to employ a replaceable tip to be used in conjunction with such pipette and afterwards to be disposed of. Typically, such replaceable tip has a main conically shaped body with a through bore starting at a large pipette receiving opening and terminating at a liquid flow port for contact with the liquid to be handled. The use of a replaceable tip advantageously avoids wetting of pipette surfaces by contaminating liquids or the inadvertent contamination of samples by the pipette itself.
As illustrated with reference to the aforementioned Walker patent, a pipette is shown wherein a piston is moved in a cylinder under manual action by an operator. The advance of the piston along the cylinder causes the displacement of volume and correspondingly results in the take-up or discharge of liquid samples depending upon the direction of movement of the piston. It can be understood from an inspection of FIG. 1 of the Walker patent that the accuracy of a pipette also depends upon the precision by which the piston is moved in the take-up stroke and that leakage between the replaceable tip and the working end of the pipette should be avoided. In some instances pipette tips have been used wherein integrally molded O rings are used to provide an enhanced seal with a pipette.
In practice, when replaceable tips are mass produced they may not always provide a precise tight fit with the pipette end. As a result, leakage occurs and accuracy of the entire pipette may suffer. Such variation in accuracy is particularly objectionable when very small quantities of liquid are to be handled.
In a co-pending patent application entitled "Manually Holdable Automatic Pipette" filed on the same day and by the same inventor as for this invention and assigned to the same assignee, a manually holdable, automatically operated pipette is described. This pipette employs an actuating mechanism and control circuit to provide a highly accurate pipette.
As described with reference to this co-pending application, the pipette's accuracy is significantly enhanced by employing a replaceable tip capable of providing a consistently high quality seal with the pipette.